JP2022150658A - Magnetic recording medium and magnetic storage device - Google Patents

Abstract

To provide a magnetic recording medium capable of having excellent electromagnetic conversion characteristics.SOLUTION: A magnetic recording medium according to the present invention includes a substrate, a ground layer, and a magnetic layer containing an alloy having an L10 type crystal structure laminated in this order. The ground layer contains MgO, the magnetic layer has at least three or more layers, when the three magnetic layers are a first magnetic recording layer, a second magnetic recording layer, and a third magnetic recording layer in order from the substrate side, Curie temperature Tc of the second magnetic recording layer is -30K to -100K lower than the Curie temperature Tc of the first magnetic recording layer and the third magnetic recording layer, respectively, and the average grain size of a bottom portion of magnetic grains forming the first magnetic recording layer is more than 15% smaller than the average grain size of the bottom portion of the magnetic grains forming the second magnetic recording layer and the third magnetic recording layer.SELECTED DRAWING: Figure 1

Description

The present invention relates to magnetic recording media and magnetic storage devices.

A magnetic recording medium generally comprises an underlayer, a magnetic layer and a protective layer laminated in this order on a substrate. As a method for recording magnetic information on a magnetic recording medium, there is a heat-assisted recording method or a microwave-assisted recording method in which the magnetic recording medium is irradiated with laser light or microwaves to locally decrease the coercive force to record magnetic information. be. Thermally-assisted recording and microwave-assisted recording can achieve two-class areal recording densities of ² Tbit/inch, so the storage capacity will increase as magnetic recording media become smaller, thinner, and have higher recording densities. It is considered as a next-generation magnetic recording method that can

As a magnetic recording medium that can be used for the thermally assisted recording system, for example, a substrate, a plurality of underlayers formed on the substrate, and a magnetic layer mainly composed of an alloy having an _L10 structure. The underlayer includes a NiO underlayer and an orientation control layer (see, for example, Patent Document 1). In this magnetic recording medium, the orientation control layer includes an underlayer made of an alloy with a BCC structure and an underlayer such as MgO having a NaCl structure, so that the NiO underlayer is (100) oriented.

When an FePt alloy having an _L10 structure is used as the magnetic layer of the magnetic recording medium, the (001) plane is used as the crystal orientation plane of the magnetic layer. In order to make the FePt alloy (001) oriented, generally (100) oriented MgO is often used as the underlayer. That is, the (100) plane of MgO has a high lattice match with the (001) plane of the FePt alloy. ) becomes easier to orient. Further, in the magnetic recording medium of Patent Document 1, MgO is used as the underlayer of the orientation control layer because the NiO underlayer is also (100) oriented.

JP 2016-26368 A

Here, the lattice constant of MgO is 0.42 nm, while that of FePt is 0.39 nm. Therefore, when the FePt film is epitaxially grown on the MgO film, a slight lattice mismatch (misfit) occurs. Tensile stress is generated in the FePt film. Since the tensile stress generated in the FePt film acts in the direction of enlarging the FePt grains, the enlarging of the magnetic grains reduces the electromagnetic conversion characteristics of the magnetic recording medium, which leads to the increase in the recording density of the magnetic recording medium. likely to interfere. In addition, the larger the grain size and the larger the contact area, the more likely it is to receive a large stress, and the larger the grain size, the greater the variation in crystal grain size, which may reduce the electromagnetic conversion characteristics of the magnetic recording medium. is high.

An object of one aspect of the present invention is to provide a magnetic recording medium that can have excellent electromagnetic conversion characteristics.

A magnetic recording medium according to an aspect of the present invention includes a substrate, an underlayer, and a magnetic layer containing an alloy having an _L10 type crystal structure laminated in this order, the underlayer containing MgO, The magnetic layer has at least three layers, and when the three magnetic layers are a first magnetic recording layer, a second magnetic recording layer and a third magnetic recording layer in order from the substrate side, The Curie temperature Tc of the second magnetic recording layer is −30 K to −100 K lower than the Curie temperatures Tc of the first magnetic recording layer and the third magnetic recording layer, respectively, and the first magnetic recording layer is 15% or more smaller than the average particle size of the bottom surface portion of the magnetic grains constituting the second magnetic recording layer and the third magnetic recording layer. .

According to one aspect of the present invention, excellent electromagnetic conversion characteristics can be obtained.

1 is a cross-sectional view showing an example of the configuration of a magnetic recording medium according to an embodiment; FIG. 1 is a TEM photograph showing an example of a cross section of a magnetic recording medium 1 according to this embodiment. 1 is a perspective view showing an example of a magnetic storage device using a magnetic recording medium according to this embodiment; FIG. 1 is a schematic diagram showing an example of a magnetic head; FIG.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail. In addition, in order to facilitate understanding of the description, the same components are denoted by the same reference numerals in each drawing, and overlapping descriptions are omitted. Also, the scale of each member in the drawings may differ from the actual scale. Unless otherwise specified, "-" indicating a numerical range in this specification means that the numerical values before and after it are included as lower and upper limits.

[Magnetic recording medium]
FIG. 1 is a cross-sectional view showing an example of the configuration of a magnetic recording medium according to this embodiment. As shown in FIG. 1, the magnetic recording medium 1 includes a substrate 10, an underlayer 20 and a magnetic layer 30 which are laminated in this order from the substrate 10 side.

In this specification, the thickness direction (perpendicular direction) of the magnetic recording medium 1 is defined as the Z-axis direction, and the lateral direction (horizontal direction) orthogonal to the thickness direction is defined as the X-axis direction. The magnetic layer 30 side in the Z-axis direction is the +Z-axis direction, and the substrate 10 side is the -Z-axis direction. In the following description, for convenience of explanation, the +Z-axis direction is referred to as upward or upward, and the −Z-axis direction is referred to as downward or downward, but this does not represent a universal vertical relationship.

Although FIG. 1 shows the underlayer 20 and the magnetic layer 30 only above the substrate 10, the magnetic recording medium 1 also has the underlayer 20 and the magnetic layer 30 stacked in this order below the substrate 10 from the substrate 10 side. be prepared.

The magnetic recording medium 1 has an underlayer 20 and a magnetic layer 30 on both upper and lower surfaces of the substrate 10, and information can be recorded on both upper and lower surfaces of the substrate 10 (double-sided recording). The substrate 10 may have the underlayer 20 and the magnetic layer 30 only on the surface of the substrate 10 so that information can be recorded only on one side of the substrate 10 (single-sided recording).

The material constituting the substrate 10 is not particularly limited as long as it is a material that can be used for magnetic recording media. Examples of materials forming the substrate 10 include Al alloys such as AlMg alloys, soda glass, aluminosilicate glass, amorphous glasses, silicon, titanium, ceramics, sapphire, quartz, and resins. Among these, Al alloys, crystallized glass, amorphous glass, and other glasses are preferable.

When manufacturing the magnetic recording medium 1, the substrate 10 may be heated to a temperature of 500° C. or higher. is preferably used.

The underlying layer 20 is provided above the substrate 10 . The underlying layer 20 comprises a layer containing MgO.

The layer containing MgO preferably contains MgO and consists essentially of MgO, and more preferably consists of MgO only. “Substantially” means that, in addition to MgO, unavoidable impurities that may be unavoidably included during the manufacturing process may be included.

In the present embodiment, since the underlayer 20 is in contact with the first magnetic recording layer 31, the (100) plane of MgO and the magnetic alloy having the _L10 structure contained in the first magnetic recording layer 31 Since lattice matching with the (001) plane is facilitated, the crystal orientation of the magnetic alloy can be enhanced.

The underlying layer 20 preferably contains a NaCl-type compound. Examples of NaCl-type compounds other than MgO include TiO, NiO, TiN, TaN, HfN, NbN, ZrC, HfC, TaC, NbC, and TiC, and two or more of them may be used in combination.

The underlayer 20 may have a multi-layer structure including other layers as long as the magnetic grains having the _L10 structure contained in the magnetic layer 30 can be oriented in the (001) plane.

The magnetic layer 30 is provided above the underlayer 20 . The magnetic layer 30 includes a first magnetic recording layer 31, a second magnetic recording layer 32, and a third magnetic recording layer 33, which are laminated in this order from the underlayer 20 side. The magnetic layer 30 may be composed of a first magnetic recording layer 31 , a second magnetic recording layer 32 and a third magnetic recording layer 33 . Also, the magnetic layer 30 may further include one or more magnetic layers other than the first magnetic recording layer 31 , the second magnetic recording layer 32 , and the third magnetic recording layer 33 .

The magnetic layer 30 includes magnetic grains having an _L10 structure. That is, the first magnetic recording layer 31, the second magnetic recording layer 32, and the third magnetic recording layer 33 included in the magnetic layer 30 contain magnetic grains having the _L10 structure.

The average grain size of the bottom portion of the magnetic grains forming the first magnetic recording layer 31 is 15 larger than the average grain size of the bottom portions of the magnetic grains forming the second magnetic recording layer 32 and the third magnetic recording layer 33. % or more, respectively, and more preferably within the range of 30% to 60%, to prevent enlargement of the magnetic particles and reduce the variation in the average particle size of the bottom surface of the magnetic particles. can do.

Here, the average particle size of the bottom portion of the magnetic particles means the average particle size of the interface portion below the magnetic particles. That is, since the grains forming the underlayer 20, the first magnetic recording layer 31, the second magnetic recording layer 32, and the third magnetic recording layer 33 grow epitaxially, these grains form continuous columnar crystals. In this columnar crystal, the average grain size at the interface between the underlayer 20 and the first magnetic recording layer 31 is taken as the average grain size at the bottom surface of the magnetic grains forming the first magnetic recording layer 31 . Let the average grain size of the interface between the first magnetic recording layer 31 and the second magnetic recording layer 32 be the average grain size of the bottom surface of the magnetic grains forming the second magnetic recording layer 32 . Let the average grain size at the interface between the second magnetic recording layer 32 and the third magnetic recording layer 33 be the average grain size at the bottom surface of the magnetic grains forming the third magnetic recording layer 33 .

In this embodiment, the average particle size of the bottom portion of the magnetic particles is determined using a scanning electron microscope (SEM) or a transmission electron microscope (TEM). For example, when the cross section of the magnetic recording layer is observed using a TEM, depth information of the cross section can be obtained because the electron beam penetrates 10 nm or more. By analyzing this cross-sectional information, the average particle size of the magnetic particles can be measured.

The Curie temperature Tc of the second magnetic recording layer 32 is -30K to -100K lower than the Curie temperatures Tc of the first magnetic recording layer 31 and the third magnetic recording layer 33, respectively. As described above, since the volume of the magnetic grains constituting the first magnetic recording layer 31 is smaller than those of the first magnetic recording layer 31 and the second magnetic recording layer 32, the magnetic field of the first magnetic recording layer 31 The characteristics are weaker than those of the second magnetic recording layer 32 in contact with the first magnetic recording layer 31 . In the present embodiment, the Curie temperature Tc of the second magnetic recording layer 32 is made smaller than the Curie temperature Tc of each of the first magnetic recording layer 31 and the third magnetic recording layer 33 within a predetermined range. , can act to enhance the magnetic properties of the first magnetic recording layer 31 . As a result, the magnetic properties of the first magnetic recording layer 31 are enhanced, and noise caused by the first magnetic recording layer 31 can be reduced.

FIG. 2 is a TEM photograph showing an example of a cross section of the magnetic recording medium 1 according to this embodiment. A magnetic recording medium shown in FIG. It has a structure laminated in this order. The three dashed lines in FIG. 2 indicate, from the lower side of the figure, the average particle size of the bottom portion of the magnetic grains constituting the first magnetic recording layer 31 and the second magnetic recording layer 32, respectively. The average grain size of the bottom surface portion of the magnetic grains and the average grain size of the bottom portion of the magnetic grains forming the third magnetic recording layer 33 are shown. Since the first magnetic recording layer 31, the second magnetic recording layer 32, and the third magnetic recording layer 33 have different compositions of constituent materials, their boundary positions can be determined from differences in contrast in TEM photographs. The average grain size of the bottom portion of the magnetic grains forming the first magnetic recording layer 31 is the average grain size of the bottom portion of the magnetic grains forming the second magnetic recording layer 32 and the average grain size of the bottom portion of the magnetic grains forming the third magnetic recording layer 33. It can be confirmed that the diameter is smaller than the average particle size of the bottom surface of the magnetic particles.

The average grain size of the bottom portion of the magnetic grains forming the first magnetic recording layer 31 is 5 more than the average grain size of the bottom portions of the magnetic grains forming the second magnetic recording layer 32 and the third magnetic recording layer 33 . % to 40%, for example, a method of using a sputtering method for film formation of the first magnetic recording layer 31 and applying a positive bias potential to the substrate 10. .

The film thickness of the first magnetic recording layer 31 is preferably 0.4 nm to 1.5 nm, more preferably 0.5 nm to 1.0 nm, even more preferably 0.6 nm to 0.8 nm. If the film thickness of the first magnetic recording layer 31 is within the above preferable range, the tensile stress generated at the interface between the first magnetic recording layer 31 and the second magnetic recording layer 32 can be endured. The magnetic recording layer 31 of 1 can exhibit magnetic properties.

In this embodiment, the film thickness of the first magnetic recording layer 31 refers to the length of the first magnetic recording layer 31 in the direction perpendicular to the main surface thereof. The thickness of the first magnetic recording layer 31 may be, for example, the thickness measured at an arbitrary location in the cross section of the first magnetic recording layer 31 . If the cross section of the first magnetic recording layer 31 is measured at several arbitrary locations, the average value of the thickness at these measured locations may be used.

The film thickness of the second magnetic recording layer 32 is preferably 0.8 nm to 3.0 nm, more preferably 1.0 nm to 2.5 nm, even more preferably 1.2 nm to 2.0 nm. If the film thickness of the second magnetic recording layer 32 is within the above preferable range, the tensile stress generated at the interface between the second magnetic recording layer 32 and the first magnetic recording layer 31 or the third magnetic recording layer 33 , the second magnetic recording layer 32 can exhibit its magnetic properties.

The film thickness of the third magnetic recording layer 33 is preferably 3 nm or more. 3.5 nm to 10.0 nm is more preferable, and 4.5 nm to 6.0 nm is even more preferable. If the film thickness of the third magnetic recording layer 33 is within the above preferable range, the tensile stress generated at the interface between the third magnetic recording layer 33 and the second magnetic recording layer 32 can be endured. The magnetic recording layer 33 of No. 3 can exhibit magnetic properties.

First magnetic recording layer 31, second magnetic recording layer 32, and third magnetic recording layer 33 By setting the film thickness of each of the first magnetic recording layers 31 within the above preferred range, each magnetic The electromagnetic conversion characteristics of the magnetic recording medium 1 can be improved because the magnetic recording medium 1 can withstand the effect of tensile stress generated at the interface between the recording layers.

As the magnetic grains having the _L10 structure contained in the magnetic layer 30, for example, FePt alloy grains, CoPt alloy grains, or the like can be used. The magnetocrystalline anisotropy constant (Ku) of the FePt alloy is 7×10 ⁶ J/m ³ or less, and the Ku of the CoPt alloy is 5×10 ⁶ J/m ³ or less, both of which are 1×10 ⁶ J. /m A material with a high Ku of ³ generations (high Ku material). Therefore, by including the FePt alloy or the CoPt alloy in the magnetic layer 30, the magnetic layer 30 can finely reduce the magnetic grains constituting the magnetic layer 30 to, for example, a grain size of 6 nm or less while maintaining thermal stability. can be

Further, the magnetic layer 30 may have a granular structure including grain boundaries.

When the magnetic layer 30 has a granular structure, the grain boundary content in the magnetic layer 30 is preferably in the range of 25% to 50% by volume, more preferably in the range of 35% to 45% by volume. . By setting the grain boundary content in the magnetic layer 30 within the above preferred range, the anisotropy of the magnetic grains contained in the magnetic layer 30 can be increased.

Here, carbides, nitrides, oxides, borides, etc. can be used for the grain boundary portion. Specific examples thereof include BN, _B4C ,C, _MoO3 , _GeO2 and the like.

The magnetic grains contained in the magnetic layer 30 are preferably c-axis oriented with respect to the substrate 10, that is, the (001) plane orientation. The method of orienting the magnetic grains contained in the magnetic layer 30 along the c-axis with respect to the substrate 10 is not particularly limited. can be done.

The magnetic recording medium 1 preferably further has a protective layer 40 on the magnetic layer 30 . The protective layer 40 has a function of protecting the magnetic recording medium 1 from damage caused by contact with a magnetic head or the like.

Examples of the protective layer 40 include a hard carbon film and the like.

Examples of the method for forming the protective layer 40 include an RF-CVD (Radio Frequency-Chemical Vapor Deposition) method in which a film is formed by decomposing a hydrocarbon gas (raw material gas) with high-frequency plasma, and a raw material gas with electrons emitted from a filament. and a FCVA (Filtered Cathodic Vacuum Arc) method of forming a film using a solid carbon target without using a raw material gas.

The thickness of the protective layer 40 is preferably 1 nm to 6 nm. When the thickness of the protective layer 40 is 1 nm or more, the flying characteristics of the magnetic head are improved, the magnetic spacing is reduced, and the SNR of the magnetic recording medium 1 is improved.

The magnetic recording medium 1 may further have a lubricant layer 50 on the protective layer 40 .

Wetting agents include, for example, fluororesins such as perfluoropolyethers.

The magnetic recording medium 1 according to the present embodiment includes a substrate 10, an underlayer 20, and a magnetic layer 30 which are laminated in this order. The underlayer 20 contains MgO, and the magnetic layer 30 is the first magnetic recording layer 31 , a second magnetic recording layer 32 and a third magnetic recording layer 33 are laminated in this order from the substrate 10 side. In the magnetic recording medium 1, the Curie temperature Tc of the second magnetic recording layer 32 is -30 K to -100 K higher than the Curie temperatures Tc of the first magnetic recording layer 31 and the third magnetic recording layer 33, respectively. The average grain size of the bottom surface portion of the magnetic grains constituting the first magnetic recording layer 31 is reduced to the average grain size of the bottom surface portions of the magnetic grains constituting the second magnetic recording layer 32 and the third magnetic recording layer 33. They are each made 15% or more smaller than the diameter. The average grain size of the bottom portion of the magnetic grains forming the first magnetic recording layer 31 is larger than the average grain size of the bottom portions of the magnetic grains forming the second magnetic recording layer 32 and the third magnetic recording layer 33. Since it is smaller by 15% or more, the magnetic properties of the first magnetic recording layer 31 are generally lower than the magnetic properties of the second magnetic recording layer 32 and the third magnetic recording layer 33 by that amount. In the present embodiment, the second magnetic recording layer 32 has a Curie temperature Tc that is lower than the first magnetic recording layer 31 and the third magnetic recording layer 33 by a predetermined range. The magnetic properties of the recording layer 32 can act to enhance the first magnetic recording layer 31 and the third magnetic recording layer 33 . Therefore, even if the magnetic properties of the second magnetic recording layer 32 and the third magnetic recording layer 33 are lower than those of the second magnetic recording layer 32 and the third magnetic recording layer 33 with which the first magnetic recording layer 31 is in direct or indirect contact, The magnetic properties of the first magnetic recording layer 31 can be enhanced by the third magnetic recording layer 33 . As a result, the magnetic properties of the first magnetic recording layer 31 are enhanced, and noise caused by the first magnetic recording layer 31 can be reduced. Therefore, the magnetic recording medium 1 can exhibit excellent electromagnetic conversion characteristics.

The electromagnetic conversion characteristics of the magnetic recording medium 1 can be evaluated from SNR (signal/noise ratio (S/N ratio)). As the SNR of the magnetic recording medium is smaller, the magnetic recording medium 1 can be evaluated to have better electromagnetic conversion characteristics. The SNR measurement is not particularly limited, and can be performed using, for example, a read/write analyzer RWA1632 and a spinstand S1701MP (both manufactured by GUZIK).

In the magnetic recording medium 1, the average grain size of the bottom surface portion of the magnetic grains forming the first magnetic recording layer 31 is set to the bottom surface portion of the magnetic grains forming the second magnetic recording layer 32 and the third magnetic recording layer 33. Magnetic grains can be included in each magnetic recording layer within a range of 30% to 60% smaller than the average grain size of . Even if the size of the magnetic grains constituting the first magnetic recording layer 31 is smaller than those of the second magnetic recording layer 32 and the third magnetic recording layer 33 within the above range, the first magnetic recording layer 31 The magnetic properties of the first magnetic recording layer 31 can be enhanced, and the noise caused by the first magnetic recording layer 31 can be reduced. Therefore, the magnetic recording medium 1 can exhibit excellent electromagnetic conversion characteristics.

In the magnetic recording medium 1, the film thickness of the first magnetic recording layer 31 can be set to 0.4 nm to 1.5 nm. As a result, the magnetic recording medium 1 can sufficiently exhibit the magnetic characteristics of the first magnetic recording layer 31, and can reliably exhibit excellent electromagnetic conversion characteristics.

In the magnetic recording medium 1, the film thickness of the second magnetic recording layer 32 can be set to 0.8 nm to 3.0 nm. As a result, the magnetic recording medium 1 can sufficiently exhibit the magnetic characteristics of the second magnetic recording layer 32, and can reliably exhibit excellent electromagnetic conversion characteristics.

In the magnetic recording medium 1, the film thickness of the third magnetic recording layer 33 can be 3 nm or more. As a result, the magnetic recording medium 1 can sufficiently exhibit the magnetic characteristics of the third magnetic recording layer 33, and can reliably exhibit excellent electromagnetic conversion characteristics.

In the magnetic recording medium ₁ , the magnetic layer 30 can contain at least one of an FePt alloy and a CoPt alloy having an L10 structure. Both FePt and CoPt alloys are high Ku materials in the order of 1×10 ⁶ J/m ³ . Therefore, by using at least one of an FePt alloy and a CoPt alloy as a material forming the magnetic layer 30, the magnetic grains forming the magnetic layer 30 can be reduced in size to, for example, 6 nm or less while maintaining thermal stability. can be miniaturized to Therefore, when the thermally-assisted recording method or the microwave-assisted recording method is used as the recording method, the magnetic layer 30 can have a coercive force of several tens of kOe at room temperature, and the magnetic layer 30 can be used for recording by the magnetic head. The magnetic field facilitates the recording of magnetic information.

[Magnetic storage device]
A magnetic storage device using the magnetic recording medium according to this embodiment will be described. The form of the magnetic storage device according to this embodiment is not particularly limited as long as it has the magnetic recording medium according to this embodiment. Here, the case where the magnetic storage device records magnetic information on the magnetic recording medium using the thermally assisted recording method will be described.

The magnetic storage device according to this embodiment includes, for example, a magnetic recording medium driving unit for rotating the magnetic recording medium according to this embodiment, a magnetic head having a near-field light generating element at its tip, a magnetic It can have a magnetic head driving section for moving the head and a recording/reproducing signal processing section.

The magnetic head is a thermally-assisted recording type magnetic head. have a wave path.

FIG. 3 is a perspective view showing an example of a magnetic storage device using the magnetic recording medium according to this embodiment. As shown in FIG. 3, the magnetic storage device 100 includes a magnetic recording medium 101, a magnetic recording medium driving section 102 for rotating the magnetic recording medium 101, and a magnetic head 103 having a near-field light generating element at its tip. , a magnetic head driving section 104 for moving the magnetic head 103, and a recording/reproducing signal processing section 105. FIG. As the magnetic recording medium 101, the magnetic recording medium 1 according to the present embodiment described above is used.

FIG. 4 is a schematic diagram showing an example of the magnetic head 103. As shown in FIG. As shown in FIG. 4, the magnetic head 103 has a recording head 110 and a reproducing head 120 .

The recording head 110 includes a main magnetic pole 111, an auxiliary magnetic pole 112, a coil 113 for generating a magnetic field, a laser diode (LD) 114 as a laser light generating section, and a near-field light generating element for generating a laser light L generated from the LD 114. and a waveguide 116 transmitting to 115 .

The read head 120 has a shield 121 and a read element 122 sandwiched between the shields 121 .

As shown in FIG. 3, in the magnetic storage device 100, the central portion of the magnetic recording medium 101 is attached to the rotating shaft of a spindle motor, and the magnetic head 103 floats above the surface of the magnetic recording medium 101 that is rotationally driven by the spindle motor. Information is written to or read from the magnetic recording medium 101 while running.

The magnetic storage device 100 according to the present embodiment can increase the recording density of the magnetic recording medium 101 by using the magnetic recording medium 1 according to the present embodiment as the magnetic recording medium 101. Therefore, it is possible to increase the recording density. can be done.

In the magnetic storage device, the magnetic head 103 may use a microwave-assisted recording type magnetic head instead of the thermally-assisted recording type magnetic head.

EXAMPLES Hereinafter, the embodiments will be specifically described with reference to Examples and Comparative Examples, but the embodiments are not limited to these Examples and Comparative Examples.

<Manufacture of magnetic recording media>
[Example 1]
A magnetic recording medium was manufactured by the following method.

A Cr-50 at % Ti alloy layer with a thickness of 100 nm and a Co-27 at % Fe-5 at % Zr-5 at % B alloy layer with a thickness of 30 nm were successively formed as underlayers on a glass substrate. Next, after heating the glass substrate to 250° C., a Cr layer with a thickness of 10 nm and an MgO layer with a thickness of 5 nm were sequentially formed. Next, after heating the glass substrate to 450° C., a 1 nm-thick FePt-40 mol % C film was formed as a first magnetic recording layer while applying a +10 V bias potential to the substrate. Next, after heating the glass substrate to 630° C., a 2 nm-thick FePt 5 at % Rh-40 mol % C film was formed as the second magnetic recording layer. Next, FePt-16SiO ₂ with a thickness of 3 nm was sequentially formed as a third magnetic recording layer. Next, a carbon film having a thickness of 3 nm was formed as a protective layer to produce a magnetic recording medium.

[Examples 2 to 10, Comparative Examples 1-1 to 1-5]
Example 1 was the same as Example 1, except that the materials constituting at least one of the first magnetic recording layer, the second magnetic recording layer, and the third magnetic recording layer were changed as shown in Table 1. A magnetic recording medium was produced in the same manner.

[Comparative Examples 2-1 to 2-5]
Example 1 is the same as Example 1, except that the temperature of the glass substrate during the deposition of the first magnetic recording layer is set to 650° C. and no bias potential is applied during the deposition of the first magnetic recording layer. Then, a magnetic recording medium was produced.

[Comparative Example 3-1]
In Example 1, the same procedure as in Example 1 was carried out, except that the material constituting the magnetic layer was changed as shown in Table 1, and no bias potential was applied during the deposition of the first magnetic recording layer. A magnetic recording medium was produced.

The cross sections of the magnetic recording media of each of the manufactured examples and comparative examples were observed with a TEM, and the average particle size of the bottom portion of the magnetic grains constituting the first magnetic recording layer and the magnetic grains constituting the second magnetic recording layer were determined. and the average grain size of the bottom portion of the magnetic grains constituting the third magnetic recording layer were measured. Table 1 shows the respective measurement results.

<Evaluation of magnetic recording medium>
(Electromagnetic conversion characteristics)
SNR (signal/noise ratio (S/N ratio)) was evaluated as the electromagnetic conversion characteristics of the magnetic recording media of each of the manufactured examples and comparative examples using a read/write analyzer RWA1632 and a spin stand S1701MP manufactured by Guzik, USA. gone.

From Table 1, in Examples 1 to 11, the SNR was 6.2 or more. On the other hand, in Comparative Examples 1-1 to 1-5, 2-1 to 2-4 and 3-1, the SNR was 5.8 or less.

Therefore, the magnetic recording media of Examples 1 to 11 differ from the magnetic recording media of Comparative Examples 1-1 to 1-5, 2-1 to 2-4 and 3-1 in that the second magnetic recording layer 32 The Curie temperature Tc of the first magnetic recording layer 31 and the Curie temperature Tc of the third magnetic recording layer 33 are respectively lower than -30 K to -100 K, and the bottom surface of the magnetic grains constituting the first magnetic recording layer 31 The average grain size of the portion was 15% or more smaller than the average grain size of the bottom portion of the magnetic grains forming the second magnetic recording layer 32 and the third magnetic recording layer 33 . As a result, the magnetic recording medium 1 can reduce the particle size of the magnetic particles contained in the magnetic layer 30, so that it can be said that excellent electromagnetic conversion characteristics can be exhibited.

As described above, the embodiment has been described, but the above embodiment is presented as an example, and the present invention is not limited by the above embodiment. The above embodiments can be implemented in various other forms, and various combinations, omissions, replacements, changes, etc. can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the scope of the invention described in the claims and equivalents thereof.

Reference Signs List 1, 101 magnetic recording medium 10 substrate 20 underlayer 30 magnetic layer 31 first magnetic recording layer 32 second magnetic recording layer 33 third magnetic recording layer 100 magnetic storage device

Claims (6)

A substrate, an underlayer, and a magnetic layer containing an alloy having an _L10 type crystal structure are laminated in this order,
The underlayer contains MgO,
The magnetic layer has at least three layers,
When the three magnetic layers are a first magnetic recording layer, a second magnetic recording layer and a third magnetic recording layer in order from the substrate side, the Curie temperature Tc of the second magnetic recording layer is , -30 K to -100 K lower than the Curie temperature Tc of the first magnetic recording layer and the third magnetic recording layer, respectively, and the average grain size of the bottom portion of the magnetic grains constituting the first magnetic recording layer A magnetic recording medium whose diameter is 15% or more smaller than the average particle diameter of the bottom portion of the magnetic grains constituting the second magnetic recording layer and the third magnetic recording layer. The average grain size of the bottom portion of the magnetic grains forming the first magnetic recording layer is larger than the average grain size of the bottom portion of the magnetic grains forming the second magnetic recording layer and the third magnetic recording layer. The magnetic recording medium of claim 1, which is 30% to 60% smaller. 3. The magnetic recording medium according to claim 1, wherein the thickness of said first magnetic recording layer is 0.4 nm to 1.5 nm. 4. The magnetic recording medium according to claim 1, wherein the second magnetic recording layer has a film thickness of 0.8 nm to 3.0 nm. 5. The magnetic recording medium according to claim 1, wherein the thickness of said third magnetic recording layer is 3 nm or more. A magnetic storage device comprising the magnetic recording medium according to any one of claims 1 to 5.

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